real life language versus textbooks

Do you find a lot of discrepancies between grammar as used in real life and as described in textbooks?

I often get this question asked by students of higher levels of both English and Spanish. And, of course, the answer is yes. This happens in all languages - it is called "Register": formal, academic, technical, colloquial, jargon, uneducated, political, educated, scientific, etc.

What is your insight on this? How many English languages can you speak and/or write? Not to mention texting and e-mailing - an entire different realm altogether!